1. Field of the Invention
The present invention relates to a semiconductor device having a package structure in which a semiconductor element is accommodated.
2. Background Art
There are known semiconductor devices which assume a package structure in which a semiconductor chip is accommodated on a package substrate made of an organic material or ceramics by a flip-chip method, die bonding method, or TAB (tape attached bonding) method, and in which the semiconductor chip is sealed by a lid made of a metal or a resin, or sealed by a two-layer structure of a heat spreader and a ring, or only by a ring provided on the package substrate.
FIG. 4 is a sectional view showing an example of such conventional semiconductor devices. In this conventional semiconductor device, a semiconductor chip 5 is, for example, flip-chip-connected to a package substrate 6 and sealed with a sealing agent 6a. And, a ring 2 and a lid 1 are laminated and bonded to the package substrate 6 with an adhesive 4 to accommodate the semiconductor chip 5 inside and protect it. The top of the semiconductor chip 5 is connected to the lid 1 with an adhesive 5a. 
FIG. 5 is a sectional view showing another example of the conventional semiconductor devices. This example does not have any member corresponding to the ring 2 shown in FIG. 4. A peripheral portion of a flat-plate portion 1a of a lid 1 extends downward to form a leg portion 1b, and the bottom face of the leg portion 1b is fixed to a package substrate 6 with an adhesive 4. The top of a semiconductor chip 5 is connected to the lid 1 with an adhesive 5a. 
FIG. 6 is a sectional view showing a further example of the conventional semiconductor devices. This example does not have any member corresponding to the lid 1 shown in FIG. 4.
Where a semiconductor device is mounted on a mounting circuit board and an enhanced heat dissipation effect is obtained by attaching radiation fins, it is advantageous in terms of heat dissipation to directly attach radiation fins to the semiconductor chip. However, in the conventional semiconductor device shown in FIGS. 4 and 5 in which the semiconductor chip is sealed by the lid or heat spreader, it is impossible to directly attach radiation fins to the semiconductor chip and it is difficult to remove the lid or heat spreader before attaching radiation fins to the semiconductor chip.
In case of the two-layer structure of the lid (or heat spreader) 1 and the ring 2, the adhesive 4 is of an epoxy resin type material, for example, and the two-layer structure can be removed, that is, peeled off, by heating the adhesive 4 to a high temperature (150xc2x0 C.). However, it is difficult to do so.
Therefore, usually, radiation fins are attached to the lid (or heat spreader) 1.
Furthermore, the semiconductor device having no lid shown in FIG. 6 has a problem of difficulty in handling: the semiconductor chip may be damaged in such handling as picking-up at the time of a test or in mounting it on a mounting circuit board.
The present invention has been made to solve the above problems in the art, and an object of the invention is therefore to provide a semiconductor device having a package structure that can be handled more properly when, for example, mounted on the mounting circuit board and that is improved in heat dissipation performance.
According to one aspect of the present invention, a semiconductor device comprises a package substrate and a semiconductor chip attached to the package substrate so as to be electrically connected to the package substrate and sealed. A ring member is attached to the package substrate surrounding the semiconductor chip. Further, a lid member is attached to the ring member to cover the semiconductor chip, and the lid member is provided so as to be able to be removed from the ring member without impairing attachment of the ring member to the package substrate.
In another aspect, in the semiconductor device, the ring member may be bonded to the package substrate with a first adhesive and the lid member may be bonded to the ring member with a second adhesive, and reduction in adhesion of the second adhesive is greater than that of the first adhesive at the time of heating.
In another aspect, in the semiconductor device, the ring member may have a groove along the inner side thereof at a position higher than a top surface of the semiconductor chip and is open on one side, and the lid member may be fitted into the groove of the ring member.
In another aspect, in the semiconductor device, the lid member may have a cap shape so as to engage with the ring member, and the lid member may be removed from the ring member through thermal expansion when heated.
Other and further objects, features and advantages of the invention will appear more fully from the following description.